1. Field of Invention
This invention relates to firearm ammunition and methods of manufacture thereof. More particularly, this invention relates to an insert for firearm ammunition which may encourage a more consistent ignition of gunpowder during firing of the ammunition.
2. Description of the Related Art
Ammunition cartridges of the type commonly used in modern firearms are generally known in the art. An ammunition cartridge typically includes a generally cylindrical case which is sized and shaped to correspond to the interior of a firing chamber of a firearm. The case includes an open leading end having a projectile held therein. When the cartridge is received within the chamber, the leading end of the case carrying the projectile faces toward and along the bore of the firearm. A primer is fixed proximate a trailing end of the case, such that the case and primer cooperate to seal the firing chamber of the firearm in all directions except toward the bore of the firearm. The primer includes a small charge of impact-sensitive, ignitable chemical mixture. When the firearm is fired, a firing pin strikes the primer and ignites the chemical mixture. The chemical mixture deflagrates to produce a jet of burning gas within the case. This burning gas is used to ignite a measure of propellant, typically gunpowder, housed within the case. When burned, the propellant produces significant quantities of gasses which push the projectile from the open end of the case, down the bore, and out from the muzzle of the firearm.
The velocity at which the projectile is discharged from the muzzle of the firearm is a function of, among other things, the quantity of propellant burned in the case, and thus the quantity of gasses produced, during the firing process, and the rate at which the propellant is burned and the gasses are produced. Thus, in order to achieve a desired velocity of the projectile from the firearm muzzle, the volume of propellant housed within the case of a given ammunition cartridge is often carefully selected and measured during manufacture of the cartridge. Typically, the volume of propellant selected for a given ammunition cartridge does not fill the entire volume of the case interior, and a void is allowed within the case.
In certain shooting situations, it is desirable to provide a measure of propellant within the case which leaves a substantial portion of the interior volume of the case void of propellant. For example, in certain shooting situations, it is desirable that the projectile fired from a firearm travel at less than supersonic velocity. This shooting situation can occur, for example, in the course of military and law enforcement activities, such as in sniper fire or other activity wherein it is desired that the location of the shooter not be detectable by reason of the sound associated with the firing of the firearm and the path of travel of the projectile. Firearm ammunition heretofore intended to provide for subsonic velocity of the projectile thereof upon firing of the ammunition traditionally has been manufactured by providing a reduced quantity of gunpowder in the case of each round of the ammunition as compared to sonic or supersonic loads of the same size and caliber. This method often leaves a very substantial portion of the interior volume of the subsonic ammunition case void of either powder and/or projectile.
In ammunition cartridges of the type described above, in which a large void is provided in the case, the propellant within the case is free to flow into one or the other end of the case, depending upon whether the firearm being used is aimed upwardly from the horizontal or downwardly from the horizontal. When the propellant shifts to the leading end of the case (adjacent the projectile and away from the primer in the closed end of the case), the jet of burning gas generated upon the firing pin striking the primer must pass through the void space between the primer and the propellant before reaching and igniting the propellant. This situation creates at least two undesirable factors, namely: (a) delay or failure in ignition of the propellant and/or (b) poor exposure of the propellant to the burning gas. The first of these factors can be so serious as to cause the shooter to believe that he has experienced a misfire, to cause the shooter to pull his/her sight off the target, and/or to damage the firearm. The second of these factors may result in insufficient ignition of the propellant and a burn pattern of the propellant which causes inconsistent propulsion of the projectile from the firearm, hence impairment of the shooter to hit a desired target at a desired velocity. When the powder shifts toward the primer-containing closed end of the case, these factors are generally reversed, causing undesirable increase in burn rate of the propellant, and corresponding increase in velocity of the projectile, as well as other deleterious results.
In light of the above, a cartridge of firearm ammunition which achieves more consistent ignition of the gunpowder within the case of the cartridge throughout a broad range of orientations of the round is desired. Other objects and advantages of the present general inventive concept will be recognized from the present specification, including the claims and the drawings appended hereto.